US astronauts begin spacewalk at orbiting lab

Two US astronauts on Sunday stepped out on the third spacewalk to prepare the International Space Station for the arrival of more commercial spacecraft in the coming years.
Barry Wilmore and Terry Virts began the spacewalk at 6:52 am (1152 GMT).
During the six hour, 45 minute outing, they plan to set up antennas and communications equipment so that future crews launching from Florida on US commercial spacecraft will be able to park at the space station, NASA said.
Another main part of their task is to route 400 feet (121 meters) of cable.
The spacewalk is the third in eight days for NASA, and is the 187th in the history of the space station.
The outing went ahead despite an apparent problem with Virts' spacesuit that allowed water to build up inside his helmet after he finished his spacewalk on Wednesday.
NASA said the suit was known to have issues with "'sublimator water carryover,' a small amount of residual water in the sublimator cooling component that can condense once the environment around the suit is repressurized following its exposure to vacuum during a spacewalk, resulting in a tiny amount of water pushing into the helmet."
US space agency experts met Friday at mission control in Houston. They said the crew was not in any danger and gave the go-ahead for Sunday's spacewalk.
The spacewalk is one of many planned for the coming year to prepare the space station for a new era in human spaceflight, when more commercial vehicles will be arriving at the research outpost carrying astronauts.
Boeing and SpaceX are working on new spaceships that will carry astronauts to space, restoring US access to low-Earth orbit following the retirement of the space shuttle program in 2011.
Boeing's crew vehicle, called CST-100, is planning its first flight with a pilot and astronaut in late 2017, and SpaceX hopes to follow soon after.
In the meantime, the world's astronauts must pay Russia $70 million per seat for transport aboard its Soyuz capsules.